1. Field of the Invention
The invention relates to display panels.
2. Description of the Related Art
Liquid crystal displays (LCDs) are used in a variety of applications, including calculators, watches, color televisions, computer monitors, and many other electronic devices. Active-matrix LCDs are a well known type of LCDs. In a conventional active matrix LCD, each picture element (or pixel) is addressed using a matrix of thin film transistors (TFTs) and one or more capacitors. The pixels are arranged and wired in an array having a plurality of rows and columns.
To address a particular pixel, the switching TFTs of a specific row are switched “on” (i.e., charged with a voltage), and then data voltage is sent to the corresponding column. Since other intersecting rows are turned off, only the capacitor at the specific pixel receives the data voltage charge. In response to the applied voltage, the liquid crystal cell of the pixel changes its polarization, and thus, the amount of light reflected from or passing through the pixel changes. In liquid crystal cells of a pixel, the magnitude of the applied voltage determines the amount of light reflected from or passing through the pixel.
Further, “System-on-glass” LCDs that allow integration of various LCD driving circuits and functions require no external integrated circuits (ICs), providing low cost, compact and highly reliable displays. The integrated driving circuits of such an LCD comprise a vertical driving circuit selecting a row of pixels and a horizontal driving circuit writing display data into each pixel in the selected row.
As shown in FIG. 1A, because of design-rule limitations in low temperature polysilicon (LTPS) processes, conventionally double RGB pixel pitch (2PP) is required to contain a set of RGB analog buffers and RGB digital to analog converters (DACs) for each RGB pixel. For example, the sampling latches may sample the data signals from the digital data bus DDB according to the control signal provided by a horizontal shift register, and the sampled data in the sampling latches is output to corresponding holding latches according the enabling signal OE. The held data signal in the holding latches are converted to RGB analog signals and output to a corresponding pixel through corresponding RGB analog buffers. Thus, a display panel requires two horizontal driving circuits disposed on the upper and lower area of the frame area respectively, as shown in FIG. 1B. However, this occupies a lot of layout area, such that panel frame size is enlarged. Moreover, in order to divide data signals from the host system for the two horizontal driving circuits, a data processing circuit 33 is further required, as shown in FIG. 1B.
As shown in FIG. 2A, another horizontal driving circuit reduces required area, with the operation timing chart thereof shown in FIG. 2B. As shown, the sampling latches sample the RGB data signals from the digital data bus DDB according to the control signal provided by the horizontal shift register, and the sampled data in the sampling latches output to corresponding holding latches according to enabling signal OE. According to the data enabling signal DE and the de-multiplexers, R data signals, G data signals, and B data signals held in the holding latches are converted to RGB analog signals by one DA converter in sequence and output to corresponding RGB pixels through one analog buffer. Namely, one DA converter and one analog buffer are shared for RGB pixels, thereby reducing required layout area for horizontal driving circuits. However, this also requires double RGB pixel pitch (2PP) for each RGB pixel driving circuit, because the sampling and holding latches dominate the width of layout of the RGB pixel driving circuit.